Using small conductors on the nanometer scale to probe electrical circuits is referred to as nanoprobing. Nanoprobing is widely used in the semiconductor market for failure analyses and device characterization. Some probes can be positioned with a resolution of better than 10 nm to measure or apply a voltage or current to electrically test a circuit.
Before probing, the sample needs to be prepared, for example, by exposing buried conductors to electrically access a circuit. A dual beam system, that is, a charged particle beam system including an ion beam column and an electron beam column, is a powerful tool for sample analysis. In a dual beam system, the ion beam can be used, for example, to expose buried layers of a circuit, and the electron beam can be used to form a highly magnified image of the exposed layers of the circuit. An advantage of some dual beam systems is that the stage can tilt and rotate to expose the work piece to the electron beam and ion beam from different angles for milling different structures and for imaging. Another advantage of some system is that a voltage can be applied to a portion of the stage to reduce the energy of the beam after the beam passes the final focusing lens and before the beam impacts the circuit, thereby reducing sample damage while maintaining high resolution.
Nanoprobe assemblies for positioning within an electron microscope are available for example from Kleindiek Nanotechnik GmbH, Reutlingen, Germany. A probe assembly can have any number of electrical probes, sometime, 4, 6, or 8, that can apply or sense a voltage from a circuit under test. Each probe includes a manipulator that can raise or lower the probe tip to contact the circuit. The probe tip is typically electrically isolated from the manipulator. When a probe assembly is mounted in the dual beam system, however, much of the flexibility of the dual beam is lost. The cabling to the probe assembly restricts the stage movement so it can be impossible to rotate and tilt the sample in a manner required for charged particle beam processing. The electronics of the probe assembly may prevent the application of a retarding voltage to the stage or sample, so that the electron beam energy cannot be reduced after passing the focusing lens.
Because the presence of the probe assembly in the dual beam system reduces the flexibility of the system, prevents rotation and beam deceleration, it is necessary to remove the work piece from the system having the probe assembly and insert it into another dual beam system to process the work piece. The work piece can then be moved back into the first system that includes the probe assembly.